1 files changed, 135 insertions, 0 deletions
diff --git a/src/hash/crc32/crc32.go b/src/hash/crc32/crc32.go
new file mode 100644
index 000000000..a2a21a06f
--- /dev/null
+++ b/src/hash/crc32/crc32.go
@@ -0,0 +1,135 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package crc32 implements the 32-bit cyclic redundancy check, or CRC-32,
+// checksum. See http://en.wikipedia.org/wiki/Cyclic_redundancy_check for
+// information.
+package crc32
+
+import (
+	"hash"
+	"sync"
+)
+
+// The size of a CRC-32 checksum in bytes.
+const Size = 4
+
+// Predefined polynomials.
+const (
+	// Far and away the most common CRC-32 polynomial.
+	// Used by ethernet (IEEE 802.3), v.42, fddi, gzip, zip, png, mpeg-2, ...
+	IEEE = 0xedb88320
+
+	// Castagnoli's polynomial, used in iSCSI.
+	// Has better error detection characteristics than IEEE.
+	// http://dx.doi.org/10.1109/26.231911
+	Castagnoli = 0x82f63b78
+
+	// Koopman's polynomial.
+	// Also has better error detection characteristics than IEEE.
+	// http://dx.doi.org/10.1109/DSN.2002.1028931
+	Koopman = 0xeb31d82e
+)
+
+// Table is a 256-word table representing the polynomial for efficient processing.
+type Table [256]uint32
+
+// castagnoliTable points to a lazily initialized Table for the Castagnoli
+// polynomial. MakeTable will always return this value when asked to make a
+// Castagnoli table so we can compare against it to find when the caller is
+// using this polynomial.
+var castagnoliTable *Table
+var castagnoliOnce sync.Once
+
+func castagnoliInit() {
+	castagnoliTable = makeTable(Castagnoli)
+}
+
+// IEEETable is the table for the IEEE polynomial.
+var IEEETable = makeTable(IEEE)
+
+// MakeTable returns the Table constructed from the specified polynomial.
+func MakeTable(poly uint32) *Table {
+	switch poly {
+	case IEEE:
+		return IEEETable
+	case Castagnoli:
+		castagnoliOnce.Do(castagnoliInit)
+		return castagnoliTable
+	}
+	return makeTable(poly)
+}
+
+// makeTable returns the Table constructed from the specified polynomial.
+func makeTable(poly uint32) *Table {
+	t := new(Table)
+	for i := 0; i < 256; i++ {
+		crc := uint32(i)
+		for j := 0; j < 8; j++ {
+			if crc&1 == 1 {
+				crc = (crc >> 1) ^ poly
+			} else {
+				crc >>= 1
+			}
+		}
+		t[i] = crc
+	}
+	return t
+}
+
+// digest represents the partial evaluation of a checksum.
+type digest struct {
+	crc uint32
+	tab *Table
+}
+
+// New creates a new hash.Hash32 computing the CRC-32 checksum
+// using the polynomial represented by the Table.
+func New(tab *Table) hash.Hash32 { return &digest{0, tab} }
+
+// NewIEEE creates a new hash.Hash32 computing the CRC-32 checksum
+// using the IEEE polynomial.
+func NewIEEE() hash.Hash32 { return New(IEEETable) }
+
+func (d *digest) Size() int { return Size }
+
+func (d *digest) BlockSize() int { return 1 }
+
+func (d *digest) Reset() { d.crc = 0 }
+
+func update(crc uint32, tab *Table, p []byte) uint32 {
+	crc = ^crc
+	for _, v := range p {
+		crc = tab[byte(crc)^v] ^ (crc >> 8)
+	}
+	return ^crc
+}
+
+// Update returns the result of adding the bytes in p to the crc.
+func Update(crc uint32, tab *Table, p []byte) uint32 {
+	if tab == castagnoliTable {
+		return updateCastagnoli(crc, p)
+	}
+	return update(crc, tab, p)
+}
+
+func (d *digest) Write(p []byte) (n int, err error) {
+	d.crc = Update(d.crc, d.tab, p)
+	return len(p), nil
+}
+
+func (d *digest) Sum32() uint32 { return d.crc }
+
+func (d *digest) Sum(in []byte) []byte {
+	s := d.Sum32()
+	return append(in, byte(s>>24), byte(s>>16), byte(s>>8), byte(s))
+}
+
+// Checksum returns the CRC-32 checksum of data
+// using the polynomial represented by the Table.
+func Checksum(data []byte, tab *Table) uint32 { return Update(0, tab, data) }
+
+// ChecksumIEEE returns the CRC-32 checksum of data
+// using the IEEE polynomial.
+func ChecksumIEEE(data []byte) uint32 { return update(0, IEEETable, data) }